A major excitatory neurotransmitter in the mammalian central nervous system (CNS) is the glutamate molecule, which binds to neurons, thereby activating cell surface receptors. These receptors can be divided into two major classes, ionotropic and metabotropic glutamate receptors, based on the structural features of the receptor proteins, the means by which the receptors transduce signals into the cell, and pharmacological profiles.
The metabotropic glutamate receptors (mGluRs) are G protein-coupled receptors that activate a variety of intracellular second messenger systems following the binding of glutamate. Activation of mGluRs in intact mammalian neurons elicits one or more of the following responses: activation of phospholipase C; increases in phosphoinositide (PI) hydrolysis; intracellular calcium release; activation of phospholipase D; activation or inhibition of adenyl cyclase; increases or decreases in the formation of cyclic adenosine monophosphate (cAMP); activation of guanylyl cyclase; increases in the formation of cyclic guanosine monophosphate (cGMP); activation of phospholipase A2; increases in arachidonic acid release; and increases or decreases in the activity of voltage- and ligand-gated ion channels. (Trends Pharmacol. Sci., 1993, 14, 13; Neurochem. Int., 1994, 24, 439; Neuropharmacology, 1995, 34, 1; Prog. Neurobiol., 1999, 59, 55).
Eight distinct mGluR subtypes, termed mGluR1 through mGluR8, have been identified by molecular cloning (Neuron, 1994, 13, 1031; Neuropharmacology, 1995, 34, 1; J. Med. Chem., 1995, 38, 1417). Further receptor diversity occurs via expression of alternatively spliced forms of certain mGluR subtypes (PNAS, 1992, 89, 10331; BBRC, 1994, 199, 1136; J. Neurosci., 1995, 15, 3970).
Metabotropic glutamate receptor subtypes may be subdivided into three groups, Group I, Group II, and Group III mGluRs, based on amino acid sequence homology, the second messenger systems utilized by the receptors, and by their pharmacological characteristics. Group I mGluR comprises mGluR1, mGluR5 and their alternatively spliced variants.
Attempts at elucidating the physiological roles of Group I mGluRs suggest that activation of these receptors elicits neuronal excitation. Evidence indicates that this excitation is due to direct activation of postsynaptic mGluRs, but it also has been suggested that activation of presynaptic mGluRs occurs, resulting in increased neurotransmitter release (Trends Pharmacol. Sci., 1992, 15, 92; Neurochem. Int., 1994, 24, 439; Neuropharmacology, 1995, 34, 1; Trends Pharmacol. Sci., 1994, 15, 33).
Metabotropic glutamate receptors have been implicated in a number of normal processes in the mammalian CNS. Activation of mGluRs has been shown to be required for induction of hippocampal long-term potentiation and cerebellar long-term depression (Nature, 1993, 363, 347; Nature, 1994, 368, 740; Cell, 1994, 79, 365; Cell, 1994, 79, 377). A role for mGluR activation in nociception and analgesia also has been demonstrated (Neuroreport, 1993, 4, 879; Brain Res., 1999, 871, 223).
Group I metabotropic glutamate receptors and mGluR5 in particular, have been suggested to play roles in a variety of pathophysiological processes and disorders affecting the CNS. These include stroke, head trauma, anoxic and ischemic injuries, hypoglycemia, epilepsy, neurodegenerative disorders such as Alzheimer's disease, acute and chronic pain, substance abuse and withdrawal, obesity and gastroesophageal reflux disease (GERD) and irritable bowel syndrome (Trends Pharmacol. Sci., 1993, 14, 13; Life Sci., 1994, 54, 135; Ann. Rev. Neurosci., 1994, 17, 31; Neuropharmacology, 1995, 34, 1; J. Med. Chem., 1995, 38, 1417; Trends Pharmacol. Sci., 2001, 22, 331; Curr. Opin. Pharmacol., 2002, 2, 43; Pain, 2002, 98, 1, Curr Top Med Chem., 2005; 5(9):897-911). Much of the pathology in these conditions is thought to be due to excessive glutamate-induced excitation of CNS neurons. As Group I mGluRs appear to increase glutamate-mediated neuronal excitation via postsynaptic mechanisms and enhanced presynaptic glutamate release, their activation probably contributes to the pathology. Accordingly, selective antagonists of Group I mGluR receptors could be therapeutically beneficial, specifically as neuroprotective agents, analgesics or anticonvulsants.
International Patent Publication No. WO 2006/120573 describes a method for inhibiting the proliferation of cancer cells in mammal by administering a therapeutically effective amount of heterocyclic mono-N-oxides.
General methods for the preparation of quinolines can be found in, e.g., International Patent Publication No. WO 2005/070890, J. Med. Chem., 2003, 46, 49 and J. Med. Chem., 2005, 48, 1107. 4-amino-3-cyano-quinoline derivatives are prepared by condensation of anilines with 2-cyano-3-ethoxy-acrylic acid ethyl ester followed by the ring closure of the obtained intermediates. Thermal ring closure affords 3-cyano-4-hydroxy-quinoline derivatives that are converted into 3-cyano-4-chloro-quinoline derivatives using phosphorous(V) oxychloride. Ring closure with phosphorous(V) oxyhalogenides directly results in 3-cyano-4-halogen-quinoline derivatives.
International Patent Publication No. WO 2005/58834 discloses quinoline derivatives for use in treating liver X receptor (LXR) mediated diseases particularly multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease and atherosclerosis, which compounds suppress Th-1 type lymphokine production, resulting in increased HDL levels, and cholesterol metabolism. The synthesis of 3-benzenesulfonyl-4-phenyl-8-trifluoromethyl-quinoline by the reaction of the appropriate aniline derivative (e.g., scheme 9 of WO 2005/58834) with 1,2-bis(benzenesulfonyl)-ethylene is described. This compound proved to be inactive on mGluR1 and mGluR5 receptors.
International Patent Publication No. WO 2005/30129 relates to compounds useful as potassium channel inhibitors. Compounds in this class may be useful as Kv1.5 antagonists for treating and preventing cardiac arrhythmias, and the like, and as Kv1.3 inhibitors for treatment of immunosuppression, autoimmune diseases, and the like.
None of the references disclose activity at the mGluR1 and/or mGluR5 receptors. Accordingly, there is a need for new compounds having activity on the mGluR1 and mGluR5 receptors.